This invention relates generally to a multi-stage valve, and in particular, to a valve suitable for use as a pressure converter in a vacuum process.
In many vacuum processes, such as vapor deposition processes, the vacuum chamber of the system is initially pumped down to a relatively low pressure (high vacuum) to rid the chamber atmosphere of any undesirable substances that might adversely affect the process. In the vapor deposition process, once the chamber has been cleared, one or more process gases may be added to the chamber atmosphere to provide an environment for maintaining or obtaining a deposition composition of predetermined character. The partial pressure (rough vacuum) of the process gases provided to the chamber is generally greater than the initial high vacuum pressure. In U.S. Pat. No. 4,172,020, a system is described for monitoring sputtering deposition parameter and achieving rapid modification of these parameters in order to obtain desired film compositions.
It is important in many vacuum applications to sample or analyze the chamber atmosphere for control purposes at the high vacuum pressures and one or more rough vacuum pressures. As illustrated in the above noted patent, a differentially pumped quadrupole mass analyzer is connected into the vacuum chamber for recovering samples of the chamber atmosphere and, in response thereto, generating control signals for regulating the process. Typically, a pressure converter is required in order to obtain sample materials at the different operating pressures. In a two-stage process, the pressure converter normally consists of two separate control valves that are interconnected by a rather complex bypass circuit that allows one of the two valves to be selectively isolated from the flow path connecting the chamber and the analyzer. Due to the complexity of the system, this type of converter is relatively expensive to construct and install. There also exists a high probability in this two-valve arrangement that one of the valves might be mispositioned thereby adversely affecting the process. When large quantities of thin film devices or the like are being manufactured during each process run, this type of loss can be relatively expensive and time consuming.